1. Field of the Invention
Embodiments disclosed here generally relate to a screening assembly for a vibratory sifter. In particular, embodiments disclosed herein relate to perforated plates for vibratory sifters. More specifically, embodiments disclosed herein relate to flanged perforated plates for vibratory sifters and methods of forming flanged perforated plates for vibratory sifters.
2. Background Art
Generally, sifters include a class of vibratory devices used to separate sized particles, as well as to separate solids from liquids. Sifters are used to screen, for example, feed material, plastic resins, and powders during industrial sorting and/or manufacturing operations.
Sifters include a filter screen through which sized materials or liquids are separated. The filter screen typically include a perforated plate base upon which a wire mesh or other perforated filter overlay is positioned. The perforated plate base generally provides structural support and allows the passage of fluids or sized material therethrough, while the wire mesh overlay defines the largest solid particle capable of passing therethrough. While many perforated plate bases are flat or slightly arcuate, it should be understood that perforated plate bases having a plurality of corrugated or pyramid-shaped channels extending thereacross may be used instead.
In certain applications, a flat smooth surface may be required for separation or sifting of materials having specific sizes or shapes. In these applications, a wire mesh overlay having a typical square filter opening may prevent materials having other desired shapes from passing through the filter. Thus, in certain applications where a particular size or shaped material may not be properly filtered through a wire mesh, a perforated plate having properly sized and shaped openings may be used to separate the material. The openings in the perforated plate may be formed by punching or stamping holes in a plate.
Because sifters may be in continuous use, repair operations and associated downtimes need to be minimized as much as possible. Often, the filter screens and/or perforated base plates of sifters, through which sized materials or liquids are separated, wear out over time and subsequently require replacement. Therefore, sifter filter screens and perforated base plates are typically constructed to be removed and replaced.
FIG. 1 shows an example of a perforated plate 10 for use in vibratory sifters. Typically, a tension ring 12 or other structural element is coupled to a lower surface 13 of the perforated plate 10 proximate an outer edge 14 of the perforated plate 10 to allow the perforated plate 10 to be mounted into a standard outer frame of a vibratory sifter (not shown). The tension ring 12 may be coupled to the perforated plate 10 by welding or chemical adhesives. However, welding of the tension ring to the perforated plated may distort thin perforated plates due to the high temperatures used in the welding process. Additionally, adhesives used for coupling the tension ring 12 to the perforated plate 10 may affect the reliability of the separator or the compatibility of the separator with certain applications where sanitary environments are required, e.g., food and pharmaceutical applications. The tension ring 12 may be formed of a wire mesh, plastic, metal, or any other material known in the art. The tension ring 12 may then be inserted into a screen retainer or screen groove (not shown) formed on an inner surface of the outer frame of the vibratory sifter (not shown). As shown in FIG. 1, the tension ring 12 may be coupled to a circumferential gasket 15. A circumferential groove 16 may be formed on an inner surface 17 of the circumferential gasket 15 and configured to receive a radially outwardly extending lip 18 formed on the tension ring 12. The circumferential gasket 15 may then be inserted into a screen retainer or screen groove (not shown) formed on an inner surface of the outer frame of the vibratory sifter (not shown).
Typically, screens used with sifters are placed in a generally horizontal fashion on a substantially horizontal bed or support structure located within a basket in the sifter. The screens themselves may be flat, nearly flat, corrugated, depressed, and/or contain raised surfaces. The basket in which the screens are mounted may be inclined towards a discharge end of the sifter. During operation, the sifter imparts a rapidly reciprocating motion to the basket and the screens. A source material, from which particles are to be separated, is poured onto a back end of the vibrating screen. The material generally flows toward the discharge end of the basket. Large particles that are unable to pass through the screen remain on top of the screen and move toward the discharge end of the basket where they are collected. Smaller particles and/or fluid pass through the screen and collect in a bed, receptacle, or pan therebeneath.
Accordingly, there exists a continuing need for a perforated plate that may be easily installed in a vibratory sifter that efficiently filters material in a sanitary and useful manner.